The turnover that we observe in the spectra of the hotspots of Cygnus A at low radio frequencies can be explained by an absorption process within the hotspots (or along the line-of-sight) and/or a cut-off in the electron energy distribution at low energies. The two most likely absorption processes are free-free absorption and synchrotron-self absorption. However, as has been discussed above, neither of these two mechanisms can account for the flattening of the hotspot radio spectra that has been seen in previous studies without unrealistic parameter values (e.g. [1]}, [2]}, [3]}). Therefore, models requiring a cut-off in the electron energy distribution at low energies have been preferred (e.g. [2]}).
